Emerging applications for radio frequency transmit/receive systems are demanding increased instantaneous bandwidth. Such applications include high-data-rate communications, low-probability-of-detection communications, simultaneous occupancy of radio frequency spectrum by multiple users, high-resolution imaging radar, low-probability-of-detection radar, wide-bandwidth electronic signals surveillance, and wide-bandwidth jamming of signals. In all these applications, it is essential for energy from the entire desired spectrum bandwidth to arrive at the receiver. In systems featuring multiple antenna elements associated with multiple signal paths in parallel, maximal energy transfer requires that the signals propagating through these multiple paths arrive at the receiver simultaneously, or as near simultaneously as possible. This does not necessarily occur naturally in a system, because various signal paths associated with various antenna elements may feature different signal propagations times, due to diverse causes such as component manufacturing tolerances and differences in signal path length, leading to offsets in signal energy arrival times.
Prior approaches to the problem of multiple signal paths causing signal returns scattered in time have used combinations of strategies such as matching various hardware units in propagation time during manufacture, selecting for use in a particular system those hardware units that as manufactured happen to feature the most similar propagation times, and propagation time measurement among various signal paths in a particular system using external measuring equipment followed by manual calibration adjustments using propagation time adjustment mechanisms in various of the system's signal paths. Where propagation time matching or calibration is not employed, the system may simply be used with its bandwidth or field of view reduced to the limits permitted by the propagation time mismatches occurring among various uncalibrated signal paths associated with various antenna elements. This last approach is particularly common for systems using the current generation of electronically scanned array or “ESA” antennas, which use phase and amplitude adjustment for beam formation and beam steering.
Prior approaches that involve propagation time measurement and calibration have required dedicated external equipment. Moreover, propagation time measurement and calibration using these approaches have required additional circuitry that bypasses the normal operating signal paths and feeds signals specially between different portions of the system for measurement. Such special bypassing and feeding leads to measurements for only a portion of the system signal paths, rather than for the entire lengths of the relevant operational signal paths, and so may leave unmeasured and uncalibrated those propagation time mismatches arising in other portions of the signal paths.